Fish mediate high food web connectivity in the lower reaches of a tropical floodplain river
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High levels of hydrological connectivity during seasonal flooding provide significant opportunities for movements of fish between rivers and their floodplains, estuaries and the sea, possibly mediating food web subsidies among habitats. To determine the degree of utilisation of food sources from different habitats in a tropical river with a short floodplain inundation duration (~2 months), stable isotope ratios in fishes and their available food were measured from three habitats (inundated floodplain, dry season freshwater, coastal marine) in the lower reaches of the Mitchell River, Queensland (Australia). Floodplain food sources constituted the majority of the diet of large-bodied fishes (barramundi Lates calcarifer, catfish Neoarius graeffei) captured on the floodplain in the wet season and for gonadal tissues of a common herbivorous fish (gizzard shad Nematalosa come), the latter suggesting that critical reproductive phases are fuelled by floodplain production. Floodplain food sources also subsidised barramundi from the recreational fishery in adjacent coastal and estuarine areas, and the broader fish community from a freshwater lagoon. These findings highlight the importance of the floodplain in supporting the production of large fishes in spite of the episodic nature and relatively short duration of inundation compared to large river floodplains of humid tropical regions. They also illustrate the high degree of food web connectivity mediated by mobile fish in this system in the absence of human modification, and point to the potential consequences of water resource development that may reduce or eliminate hydrological connectivity between the river and its floodplain.
KeywordsStable sulfur isotopes Flood pulse Liver Gonad Income breeding
The authors thank Richard Hunt, Dominic Váldez, Stephen Faggotter, Courtenay Mills, Kate Masci, Alisha Steward, Colton Perna, Michael Pusey, Raven Greenwool, Anzac Frank, Taron David and Michael Gater for assistance with sample collection, Jeff Shellberg and Doug Ward for hydrology data, and Rene Diocares, Vanessa Fry and Laura Jardine for help with sample processing and isotope analysis. This work was conducted under the Tropical Rivers and Coastal Knowledge (TRaCK) Research Hub. TRaCK received major funding for its research through the Australian Government’s Commonwealth Environment Research Facilities initiative; the Australian Government’s Raising National Water Standards Program; Land and Water Australia; the Fisheries Research and Development Corporation, and the Queensland Government’s Smart State Innovation Fund.
- Hunt RJ, Jardine TD, Hamilton SK, Bunn SE (2011) Temporal and spatial constraints on ecosystem metabolism and food web carbon transfer in a wet-dry tropical river. Freshw Biol (accepted)Google Scholar
- Jardine TD, Pettit NE, Warfe DM, Pusey BJ, Ward DP, Douglas MM, Davies PM, Bunn SE (2011) Consumer–resource coupling in wet-dry tropical rivers. J Animal Ecol (accepted)Google Scholar
- Junk WJ, Wantzen KM (2004) The flood pulse concept: new aspects, approaches and applications—an update. In: Welcomme RL, Petr T (eds) Proceedings of the Second International Symposium on the Management of Large Rivers for Fisheries. FAO Regional Office for Asia and the Pacific, BangkokGoogle Scholar
- Junk WJ, Bayley PB, Sparks RE (1989) The flood pulse concept in river–floodplain systems. In: Dodge DP (ed) Proceedings of the International Large River Symposium (Canadian Special Publication of Fisheries and Aquatic Sciences). Canadian Government Publishing Centre, Ottawa, pp 110–127Google Scholar
- Lewis WM, Hamilton SK, Saunders JF (1995) Rivers of northern South America. In: Cushing CE, Cummins KW, Minshall GW (eds) River and stream ecosystems. Elsevier, Amsterdam, pp 219–256Google Scholar
- Pusey B, Kennard M, Arthington A (2004) Freshwater fishes of North-Eastern Australia. CSIRO, CollingwoodGoogle Scholar
- Sogard SM (1997) Size-selective mortality in the juvenile stage of teleost fishes: a review. Bull Mar Sci 60:1129–1157Google Scholar
- Ward D, Brooks A, Pusey B, Olley J, Shellberg J, Tews K, Spencer J, Knight J (2011) Riverine landscapes and aquatic systems diversity. In: Pusey B (ed) Aquatic biodiversity in northern Australia: patterns, threats and future. Charles Darwin University Press, Darwin, pp 5–22Google Scholar
- Welcomme RL (2001) Inland fisheries: ecology and management (Food and Agriculture Organization). Blackwell, OxfordGoogle Scholar
- Welcomme RL, Halls A (2003) Dependence of tropical river fisheries on flow. In: Welcomme RL, Petr T (eds) Proceedings of the Second International Symposium on the Management of Large Rivers for Fisheries. FAO Regional Office for Asia and the Pacific, Bangkok, pp 267–283Google Scholar
- Winemiller KO, Jepsen DB (1998) Effects of seasonality and fish movement on tropical river food webs. J Fish Biol 53(Suppl A):267–296Google Scholar